It is known to produce molded parts (dashboards as part of the interior fittings of motor vehicles, for example) in accordance with the powder-slush process. In this case a mold, corresponding for example to the three-dimensional shape of a dashboard, is heated and coupled together with a powder pan.
By rotating the unit formed from mold and powder pan, distribution of the PVC powder capable of forming a gel takes place, which is brought into contact with the hot mold and adheres controlling the rotation.
Following the end of rotation, i.e. after the powder has been deposited on the heated surface of the inner wall of the mold, the powder pan is separated from the mold and the phases of sintering and gelling of the powder in the mold follow.
The mold is cooled after the powder adhering to the mold has been sintered together and a slush skin has formed. The slush skin is subsequently removed from the mold.
The powder-slush process described up to this point assumes that the slush skin which was formed is of a single color, because only one particular PVC powder is used over the entire area of the mold. However, actually there is often a requirement to embody molded parts, in particular dashboards for the interior fitting of motor vehicles, in several colors, i.e. with areas of different colors. It is intended to keep the powder-slush process for doing this, since it has been generally successful in connection with the production of slush skins.
Masking techniques constitute a known possibility. If, for example, a two-colored slush skin is desired, a color zone corresponding to a first color area is covered with a mask in the mold, so that only the other color zone corresponding to the second color area is free. A part of the slush skin is then produced in this color zone using PVC powder with the desired second color.
Subsequently the opposite operation is performed, i.e. now the already produced partial slush skin in the second color zone is covered with another mask, so that the first color zone in the mold is free, where now the second part of the slush skin is produced using another PVC powder with the first color. The masks are embodied in such a way that a narrow transition area is formed between the individual color zones, so that during the production of separating seam with the previously produced first part of the slush skin, a one-piece slush skin is created.
Although the masking technique is basically usable for producing multicolored slush skins, it has been shown in actuality that the separating seam looks untidy to the eye. But it is the separating seam itself, extending between the different color areas, which is the decisive criterion for a multicolored slush skin which looks tidy to the eye.
While the parts of the slush skin with the different colors are produced at different times when using the masking technique, it is already known from EP 0 162 594 A2 to produce these color areas at the same time in one mold. For this purpose different chambers or color zones delimited by separation fins are formed in the mold, into which the diverse PVC powders with the appropriate desired colors are introduced. The separation fins are embodied such that a one-piece slush skin has been created at the end of the powder-slush process.
Although by means of this technique it is possible to shorten the amount of time for producing a multicolored slush skin, it was also found in this case that the separating seams are not tidily made, which as a result is not pleasing to the eye of the user.
Finally, it is also possible to produce the separate skin pieces of different colors separately and to combine these individual parts later into a uniform slush skin, for example by connecting the individual parts by HF welding. If the slush skin has a three-dimensional shape, however, HF welding is difficult and an untidy weld seam can appear. It is also possible to connect the individual skin parts by gluing. But this process is also complicated with three-dimensional skins and results in untidy separating seams. There is furthermore the danger that the adhesive may fail, for example if a multicolored dashboard is exposed to temperature extremes in winter and summer. In the summer the extended exposure to the rays of the sun can easily cause the adhesive to loosen.